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--0000000000006f7447056715c725 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Interesting discussion - thank you! And then there is Wikipedia re interesting research going on: https://en.wikipedia.org/wiki/Lemnoideae "Duckweed is being studied by researchers around the world as a possible source of clean energy. In the United States, in addition to being the subject of study by the DOE, both Rutgers University <https://en.wikipedia.org/wiki/Rutgers_University> and North Carolina State University <https://en.wikipedia.org/wiki/North_Carolina_State_University> have ongoing projects to determine whether duckweed might be a source of cost-effective, clean, renewable energy <https://en.wikipedia.org/wiki/Renewable_energy>.[18] <https://en.wikipedia.org/wiki/Lemnoideae#cite_note-18>[19] <https://en.wikipedia.org/wiki/Lemnoideae#cite_note-19> Duckweed is a good candidate as a biofuel because it grows rapidly, produces five to six times as much starch as corn per unit of area, and does not contribute to global warming.[20] <https://en.wikipedia.org/wiki/Lemnoideae#cite_note-20>[21] <https://en.wikipedia.org/wiki/Lemnoideae#cite_note-21> Unlike fossil fuels, duckweed removes carbon dioxide from the atmosphere instead of adding it.[22]" <https://en.wikipedia.org/wiki/Lemnoideae#cite_note-22> Nancy On Sat, Mar 10, 2018 at 3:52 PM, David <dwebster@glinx.com> wrote: > Hi Steven & All, > Good points. Aquatic plants typically have specialized tissues of > interconnected passages which are filled with gas when the plant is activ= e > and I would expect this to be true of Lemna also. The relative solubility > of CO2 and O2 in water is no doubt relevant; CO2 is 16.4 and 31.5 times a= s > soluble in water as O2 at 0o C and 10oC respectively. So during the growi= ng > season, photosynthesis would keep such aerenchyma filled with O2. With > shorter days and less photosynthesis, CO2 production by respiration (yea= r > round in all living tissue night and day) would gradually exceed O2 > production and lead to a flooding of the ballast tanks as the CO2 > dissolves; submarine down. > No doubt details of the anatomy play a part but I would expect stomat= a > if present to be on the upper surface. > Yt, DW,Kentville > > > ------ Original Message ------ > From: "Stephen Shaw" <srshaw@Dal.Ca> > To: "naturens@chebucto.ns.ca" <naturens@chebucto.ns.ca> > Sent: 3/10/2018 3:20:47 PM > Subject: Re: [NatureNS] Duckweed > > Interesting puzzle, perhaps not so simple. Any cell system like a live > leaf is bound to be somewhat denser than pond water, regardless of denser > starch, so will naturally sink at all times unless kept buoyant by the > extracellular gas bubbles or some other modification. What seems to need > explaining is why the bubbles are maintained in summer (dissolved gases c= an > pass through lipid cell membranes quickly, so you=E2=80=99d expect them t= o dissolve > out into the surrounding pond), and why they disappear in winter. He > doesn=E2=80=99t seem to know if it=E2=80=99s CO2 or O2 in the bubbles, or= both. Perhaps > they are largely O2 in summer and dissolve and normally pass out of the > leaf to oxygenate the pond and dissolved CO2 moves in, but leaf > photosynthesis is sufficiently high in summer to maintain them, despite > these losses. In winter gas production simply stops, and the non-buoyant > plants sink. As winter ends, respiration produces bubbles with a differe= nt > gas, CO2, and they rise again then switch over to O2 as photosynthesis > picks up. > > It therefore seems likely that these leaves have some special surface > coating that slows down gas exchange with the pond. Maybe they still > retain stomata under the leaf which normally facilitate gas exchange for > leaves in air, but these are modified to block or regulate gas exchange i= n > water? Maybe this is already known, just not to us here? > Steve > > On Mar 10, 2018, at 10:45 AM, David <dwebster@glinx.com> wrote: > > Hi Nancy & All, > I admit not having wondered about this but I think he makes a simple > process complicated. The air pockets to which he refers are presumably > intercellular spaces which in the absence of photosynthesis presumably ca= n > become water filled. Starch has a specific gravity of 1.5 g/mL and, in > cooler weather starch will accumulate when respiration slows more than > photosynthesis and the submarine will sink. With warming, growth resumes, > respiration and starch consumption rates increase and the submarine rise= s. > Yt, DW, Kentville > > ------ Original Message ------ > From: "nancy dowd" <nancypdowd@gmail.com> > To: naturens@chebucto.ns.ca > Sent: 3/10/2018 9:08:02 AM > Subject: [NatureNS] Duckweed > > This is an interesting article on Duckweed seasonal disappearance and > reappearance in the Spring 2018 issue of Northern Woodlands Magazine. > https://northernwoodlands.org/outside_story/article/duckweed-migration > > I had never really thought about where it went in Fall or how it > re-emerges in Spring. Such an important floating pond plant in productive > fresh water > > Nancy D > > Sent from my iPad > > > --=20 Nancy Robinson 514-605-7186 --0000000000006f7447056715c725 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><div>Interesting discussion - thank you!=C2=A0=C2=A0 <br><= br>And then there is Wikipedia re interesting research going on:=C2=A0 <a h= ref=3D"https://en.wikipedia.org/wiki/Lemnoideae" target=3D"_blank">https://= en.wikipedia.org/wiki/<wbr>Lemnoideae</a><br></div><div><br>"Duckweed = is being studied by researchers around the world as a possible=20 source of clean energy. In the United States, in addition to being the=20 subject of study by the DOE, both <a href=3D"https://en.wikipedia.org/wiki/= Rutgers_University" title=3D"Rutgers University" target=3D"_blank">Rutgers = University</a> and <a href=3D"https://en.wikipedia.org/wiki/North_Carolina_= State_University" title=3D"North Carolina State University" target=3D"_blan= k">North Carolina State University</a> have ongoing projects to determine w= hether duckweed might be a source of cost-effective, clean, <a href=3D"http= s://en.wikipedia.org/wiki/Renewable_energy" title=3D"Renewable energy" targ= et=3D"_blank">renewable energy</a>.<sup id=3D"m_5749390366674581471gmail-ci= te_ref-18" class=3D"m_5749390366674581471gmail-reference"><a href=3D"https:= //en.wikipedia.org/wiki/Lemnoideae#cite_note-18" target=3D"_blank">[18]</a>= </sup><sup id=3D"m_5749390366674581471gmail-cite_ref-19" class=3D"m_5749390= 366674581471gmail-reference"><a href=3D"https://en.wikipedia.org/wiki/Lemno= ideae#c